In recent years, the use of advanced composite structures has experienced tremendous growth in the aerospace, automotive, and many other commercial industries. While composite materials offer significant improvements in performance, they require strict quality control procedures in both the manufacturing processes and after the materials are in service in finished products. Specifically, non-destructive evaluation (NDE) methods must assess the structural integrity of composite materials. This assessment detects inclusions, delaminations and porosities. Conventional NDE methods are slow, labor-intensive, and costly. As a result, testing procedures adversely increase the manufacturing costs associated with composite structures.
Various methods and apparatuses have been proposed to assess the structural integrity of composite structures. One solution uses an ultrasonic source to generate ultrasonic surface displacements in a work piece which are then measured and analyzed. Often, the external source of ultrasound is a pulsed generation laser beam directed at the target. Laser light from a separate detection laser is scattered by ultrasonic surface displacements at the work piece. Then collection optics collect the scattered laser energy. The collection optics are coupled to an interferometer or other device, and data about the structural integrity of the composite structure can be obtained through analysis of the scattered laser energy. Laser ultrasound has been shown to be very effective for the inspection of parts during the manufacturing process.
However, the equipment used for laser ultrasound is custom-designed and is presently a limiting factor regarding inspection speed. Previous generation lasers used were either flash-lamp pumped rod architectures, diode-pumped slab configurations, or gas lasers.
It is important to note that all of the various ultrasound generation laser architectures described here are by their nature large and heavy. Therefore, these architectures are unsuited to use in portable laser ultrasound inspection systems for any sort of in-service, remote, or in-the-field deployment. In addition, because they are so large and heavy, these architectures require substantial robotic fixturing and complex beam delivery systems even when they are deployed in factory environments, all of which greatly increases the initial overall cost of the laser ultrasound inspection system as well as the maintenance costs to keep the inspection system in operation in a production environment. These large complex structures are suited to external component inspections and cannot inspect all facets of assembled structures.